1. Field of the Invention
This invention relates to a process for converting a heavy hydrocarbon, particularly a heavy oil such as an atmospheric residue or a vacuum residue of crude oils, highly into lighter and more valuable product, and a process for further hydrotreating the lighter hydrocarbon oil, and also to a process for producing gaseous olefins and monocyclic aromatics from a heavy hydrocarbon as the feedstock by using these processes.
2. Description of the Prior Art
In recent years, in addition to the trend of converting crude oils to heavy oils, unbalance between the demand and the supply of petroleum products accompanied by the increase in demand of lighter oils is arousing social problems, and effective utilization of excessive heavy oils is nowadays an issue of crucial importance in the field of petroleum industries.
On the other hand, in production of gaseous olefins such as ethylene, propylene, butadiene, etc. and monocyclic aromatics such as benzene, toluene, xylene, etc., light hydrocarbons such as oil field gases or petroleum refinery by-products such as naphtha have been primarily employed. These are now suffering from shortage of supply with their costs being increased, and economical advantages to obtain gaseous olefins or monocyclic aromatics are becoming markedly lowered. Accordingly, in order to solve such a problem related to the structure of industries, various attempts have recently been made to produce petrochemical starting materials by hydrotreating lighter oils such as kerosenes, gas oils, vacuum gas oils, etc. followed by steam pyrolysis. However, in these methods, various kinds of oils employed as the feedstock are available as petroleum products, and the situation of starting material supply is the same as in the case of the light hydrocarbon such as naphtha.
Thus, in either petroleum industries or petrochemical industries, it is now an important task to convert a heavy oil into lighter and more valuable product for effective utilization as light petroleum products or starting materials for petroleum chemistry. Accordingly, a number of processes have been proposed for hydrocracking or thermal cracking of heavy oils, but none of these processes are not necessarily satisfactory for converting a heavy oil such as a vacuum residue into lighter product, since some drawbacks are involved.
For example, in a fixed-bed or fluidized-bed hydrocracking process in which the reaction is conducted in a reactor packed with a granular or powderly catalyst, when high conversion to lighter product is effected, by-produced carbon and metal components contained in the feedstock oil will be gradually deposited on the catalyst layer, whereby depletion in activity of the catalyst or plugging of the catalyst layer may be brought about.
On the other hand, when it is desired to accomplish high conversion of a heavy hydrocarbon to lighter product according to thermal cracking, so called coking phenomenon will be caused, which will lead to stopping of the operation. Therefore, this process is generally applicable only to conversion to lighter product to an extent such that coking poses no problem. For improvement of this point, the so called hydrobisbreaking process has been proposed. This process, however, cannot give sufficient coking inhibition effect even if the hydrogen pressure is increased to a high pressure of 300 kg/cm.sup.2. The coker process is also proposed, in which conversion to lighter product is conducted while forming positively cokes. This process, in addition to the disposal of cokes by-produced in a large amount, cannot be free from the problem of lowered yield of light oil. Besides, the light oil obtained is enriched in aromatic components and olefin components, thus involving the drawback of poor quality.
Thus, in the prior art, even when attempted to convert a high boiling material into lighter product by catalytic processing of a heavy oil, impurities contained in the oil such as sulfur or heavy metals as a matter of course, particularly the presence of basic polymer compounds will markedly lower the acidic ability of the catalyst. As the result, there is involved the problem that the cracking activity due to acidity of the catalyst cannot persist. Also, in thermal cracking of a hydrocarbon in absence of catalyst, the reaction rate is known to be greater as its molecular weight is greater. However, since the reaction rates of side reactions such as cokes formation and polycondensation are also great, it is very difficult in reaction operations to increase the degree of cracking.
On the other hand, various techniques have been reported for hydrotreating heavy hydrocarbons by the reaction in a dispersed state with addition of solid materials. U.S. Pat. Nos. 3,131,142, 4,134,825, 4,172,814 and 4,285,804 disclose hydrotreatments by adding an oil-soluble metal compound or an emulsion of an aqueous solution of a water-soluble metal compound. U.S. Pat. Nos. 3,161,585 and 3,657,111 disclose hydrotreatments by using a thermally cracked colloidal material of an oil-soluble metal compound or vanadium sulfide colloid particles. Canadian Pat. Nos. 1,073,389, 1,076,983, U.S. Pat. Nos. 4,176,051, 4,214,977 and 4,376,695 disclose hydrocracking by using pulverized coal or pulverized coal coated with a metal salt. U.S. Pat. Nos. 3,707,461 and 4,299,685 disclose hydrotreatments by use of pulverized coal ash. U.S. Pat. Nos. 4,169,038, 4,178,227, 4,204,943, Japanese Laid-open Patent Publication Nos. 207688/1982 and 69289/1983 disclose hydrotreatments by using cokes by-produced or petroleum ash by-produced. Japanese Laid-open Patent Publication Nos. 40806/1979 141388/1981 disclose hydrocracking by using a desulfurized catalyst or a pulverized waste catalyst thereof. U.S. Pat. Nos. 4,066,530 and 4,067,799 disclose hydrotreatment by use of a combination of an oil-soluble metal compound and an iron component particle, Japanese Laid-open Patent Publication No. 108294/1983 by use of a combination of a metal compound and a metal-containing dust by-produced, and U.S. Pat. Nos. 3,331,769 and 4,376,037 by use of a combination of a metal compound and a porous solid catalyst or a porous carrier, respectively. However, most of these techniques employ the reactions approximate to desulfurization conditions, and they are proposals aiming at primarily metal removal, hetero-atom removal such as sulfur or nitrogen removal or residual carbon removal from heavy hydrocarbons. A part of these techniques employ a heavy hydrocarbon which can be cracked with relative ease as the feedstock and attempt to apply an appropriate degree of hydrocracking by utilizing a waste catalyst, cokes by-produced or a natural product. Thus, according to any of these techniques, when applied for high conversion of heavy hydrocarbons such as atmospheric residue or vacuum residue into lighter products, the technical problems from practical aspect such plugging of equipments and economical problems remain to be solved.